1. Field of the Invention
The present invention relates to a solid-state imaging device and a manufacturing method of a solid-state imaging device. The present invention also relates to an electronic device employing a solid-state imaging device.
2. Description of the Related Art
A solid-state imaging device is largely classified into a CCD (Charge Coupled Device) solid-state imaging device and a CMOS (Complementary Metal Oxide Semiconductor) solid-state imaging device.
In these solid-state imaging devices, a light-receiving portion formed of a photo diode is provided to each pixel and signal charges are generated in the light-receiving portion by photoelectric conversion of light incident on the light-receiving portion. In a CCD solid-state imaging device, signal charges generated in the light-receiving portion are transferred inside a charge transfer portion having a CCD structure and outputted from an output portion after they are converted to a pixel signal. Meanwhile, in a CMOS solid-state imaging device, signal charges generated in the light-receiving portion are amplified pixel by pixel and the amplified signal is outputted to a corresponding signal line as a pixel signal.
In order to prevent leakage of signal charges between adjacent pixels, the solid-state imaging device is provided with a well region for element isolation in a region between one pixel and an adjacent pixel. JP-A-2004-165462 describes a CCD solid-state imaging device configured in such a manner that an element isolation region made up of a multi-stage impurity region is formed between respective adjacent pixels.
According to this CCD solid-state imaging device, when an element isolation region made up of a multi-stage impurity region is formed by ion implantation, anion implantation area to form a lower-layer impurity region is made smaller than an ion implantation area to form an upper-layer impurity region. In this case, charge accumulation regions in the light-receiving portion become the same in the depth direction at the finishing stage after diffusion. Accordingly, because the element isolation region is formed as an impurity region that gradually narrows in the depth direction of the semiconductor substrate, it becomes possible to suppress a decrease of the charge accumulation region in the light-receiving portion caused by diffusion in the impurity region.